geographical accuracy

Andy Armstrong andy at
Sat Feb 24 15:05:46 GMT 2007

On 24 Feb 2007, at 13:45, Graham Seaman wrote:
> The partial solution (a better one would be to rewrite one of the  
> perl modules..): download the document 'Transformations and OSGM02  
> User Guide' from the gps.ordnancesurvey site. Apply the iterative  
> transformation titled 'inverse transformation (OSGB36 to  
> ETRS89)'  (page 22) to your OS eastings and northings, using the  
> lookup tables provided in the zip file with the document. Use the  
> resulting  ETRS89  eastings and northings as input to either of the  
> two perl modules. Result: on a quick sample of the outputs, I'm  
> getting around 4 to 5 decimal places of agreement with google and  
> the reference converter. Not perfect, but good enough for what I  
> need..

Glad you got it sorted.

I have a Perl implementation here that I derived from the information  
on the OS site. That gets ~5 DP of accuracy compared with's conversion. I guess I should release it.

Andy Armstrong,

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